The present invention relates to adhesive tapes. In particular, the present invention relates to an adhesive tape having a foam-like backing, at least one layer of heat-activated adhesive on at least one side thereof, and, optionally, at least one layer of pressure-sensitive adhesive on the side thereof opposite the layer of heat-activated adhesive, and to a process for making the tape.
Single- and double-sided adhesive tapes are known which have a heat-activated adhesive on the first side of a compressible backing and, for double-sided tapes, a pressure-sensitive adhesive on the second side of the backing. Typically, the compressible backing is a foam backing wherein the backing has a cellular structure consisting of gas pockets dispersed throughout the backing. One of the deficiencies of the prior art is the limited range of surfaces to which they will bind. Furthermore, the backing and heat-activated adhesive may become separated because the adhesive is typically laminated or coated directly on a pre-fabricated foam backing, and conventional foam backings break apart under stress and over time.
Heat-seal adhesives are dry coatings on the back of flexible laminates. They are heat sealed to panels by rollers or quick presses at elevated temperatures and pressures. These adhesives may be applied and dried by the laminate producer using water or solvent based polymers. Heat seal adhesives adhere to most surfaces and form very tough bonds.
U.S. Pat. No. 5,922,428 issued to Pufahl on Jul. 13, 1999 shows a sterilizable package with an improved seal. The package utilizes an adhesive tape having a first adhesive layer formed from a heat-seal adhesive, and a second adhesive layer formed from a pressure-sensitive adhesive. A carrier layer composed of a polyester or other polymeric material is disposed between the two adhesive layers. The heat-seal adhesive is applied to the carrier layer in a molten state. Because the carrier layer is already fully polymerized, the heat-seal adhesive layer may become separated therefrom.
A hot-melt adhesive, on the other hand, is an adhesive which is a 100% solids thermoplastic and is applied molten to form a bond upon cooling. Hot melts differ from conventional liquid adhesives because they set by cooling rather than by absorption or evaporation. It is well-known to pre-coat liners with the hot-melt adhesive and then reactivate the adhesive by heat. Furthermore, it is conventional to utilize the pre-coated liners to laminate the hot-melt onto another substrate.
Hot-melt adhesives are employed in many nonstructural applications. Based on thermoplastic resins, which melt at elevated temperatures without degrading, these adhesives are applied as hot liquids to an adherend. Hot-melts are non-volatile adhesives that are solid at room temperature, liquify upon heating, and resolidify with cooling forming nearly instantaneous bonds. These adhesives are widely used in the automotive and home-appliances fields.
U.S. Pat. No. 5,322,709 issued to Lulla et al. on Jun. 21, 1994 discloses a process for production of a pressure sensitive hot melt-adhesive coated tape, which process incorporates a blowing agent into the hot-melt adhesive, and subsequently decomposes the blowing agent forming a hot melt coating having a cellular structure. The process involves coating the hot melt adhesive composition onto a paper or plastic film tape backing either via extrusion or a line technique. The invention of Lulla et al. applies the hot-melt adhesive directly to the pre-fabricated tape backing as a coating thereon, which does not address the concern that the adhesive and a foam backing may become separated during use.
U.S. Pat. No. 5,605,717 issued to Simmons et al. on Feb. 25, 1997 describes a process for foaming a hot-melt adhesive using moisture in a backing. The hot-melt adhesive is extruded onto a coextrudate (the backing material) and as the water in the coextrudate evaporates self-contained bubbles of water vapor are formed in the adhesive producing a foamed hot-melt adhesive on a backing. Foamed hot-melt adhesives are inherently less reliable than non-foamed hot-melt adhesives, as they are more brittle.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed.